Nitrogen accumulation and partitioning in hail‐damaged soybeans¹

Cooperative investigation of USDA‐ARS and the Minnesota Agric. Exp. Stn. (Scientific Journal Series No. 14046). This research was supported in part by the Minnesota Soybean Research and Promotion Council.

Abstract

Hail damage to an experiment that was being used to investigate nitrogen (N) nutrition of soybeans [Glycine max (L.) Merr.] with ¹⁵N methodology provided a unique opportunity to study the effects of hail damage at the R3 stage of development on N uptake and partitioning through stage R5.8. Field plots were established on a silt loam soil (Typic Hapludol 1). Severely damaged (mean 72% leaf loss) and slightly damaged (mean 26% leaf loss) soybeans were compared for total reduced N and for ¹⁵N concentration in leaflets, petioles, stems, roots, pod walls, and seeds during the 28 days following the hailstrom. The concentration of total N and of ¹⁵N in all organs in both damage treatments declined significantly after the storm, but less in green leaflets (total N), and in green leaflets, green petioles, and pod walls (¹⁵N) of severely than of slightly damaged plants. Measurements on senesced leaflets and petioles showed that the concentration of ¹⁵N also decreased to a greater extent than that of the total N in these organs. This differential loss of ¹⁵N compared with total N suggests that the ¹⁵N was in a form that was less refractory than was the bulk tissue N, and provides evidence of separate mobile pools of N in the plant. Nitrogen budgets were calculated to compare the loss of N and ¹⁵N from abscising leaflets and petioles to the N accumulation of the damaged plants during podfill. These showed that loss from the leaflets and petioles contributed only 7% of the total N accumulated by the plants between R3 and R5.8. This study has exemplified the usefulness of ¹⁵N methodology in investigations of the nutrition and physiology of soybeans suffering leaf damage by hail.

Key words:

• defoliation
• N metabolism
• source‐sink relations
• ¹⁵N
• N mobilization
• Glycine max (L.) Merr.

Notes

Cooperative investigation of USDA‐ARS and the Minnesota Agric. Exp. Stn. (Scientific Journal Series No. 14046). This research was supported in part by the Minnesota Soybean Research and Promotion Council.

Former Graduate Research Assistant (Present address: EMBRAPA/ CNPAF, Caixa Postal 179, 74.000 Goiania, Goias, Brasil) and Plant Physiologist, USDA‐ARS.